A modular cart assembly includes a first carrier unit that may contain an animal. A pair of wheels is provided. Each of the wheels is rotatably coupled to the first carrier unit. Thus, the first carrier unit may roll along a support surface. A first handle is coupled to the first carrier unit and the first handle may be manipulated. A pair of second carrier units is provided. Each of the second carrier units may contain an animal. Each of the second carriers units is selectively stacked on the first carrier unit. Thus, each of the second carriers units is transportable with the first carrier unit.
